1. Technical Field
The present invention relates to a semiconductor device and a method of manufacturing a semiconductor device.
2. Related Art
Conventionally, a vertical semiconductor device in which an anode and a cathode are provided to the front surface and rear surface of a semiconductor substrate has been known. The semiconductor device is used for example as a FWD (free wheeling diode) (see Patent Document 1, for example). Related prior art documents include the following documents.
Patent Document 1: Japanese Patent Application Publication No. 2012-199577
Patent Document 2: WO 2013/100155
Patent Document 3: U.S. Pat. No. 6,482,681
Patent Document 4: U.S. Pat. No. 6,707,111
Patent Document 5: Japanese Patent Application Publication No. 2001-160559
Patent Document 6: Japanese Patent Application Publication No. 2001-156299
Patent Document 7: Japanese Patent Application Publication No. H7-193218
Patent Document 8: United States Patent Application Publication No. 2008-1257
Patent Document 9: United States Patent Application Publication No. 2008-54369
Preferred characteristics of the above-mentioned semiconductor device include a low reverse recovery loss (that is, a low peak current Irp of a reverse recovery current and a low tail current of a reverse recovery current) and gentle reverse recovery (that is, a gentle rate of temporal change dV/dt of reverse recovery voltage). These characteristics are influenced by the carrier lifetime distribution in the direction vertical to the front surface of the semiconductor substrate. Methods of controlling a carrier lifetime include a technique of irradiating the inside of a semiconductor substrate with an electron ray. But when the carrier lifetime is controlled by electron ray irradiation, the carrier lifetime inside the semiconductor substrate becomes short uniformly. In this case, the tail current can be made small. But dV/dt and Irp tend to be large.